The present invention relates to a new and improved construction of marine reversing gearing or power transmission system for vessels or the like.
The marine reversing gearing of the present invention is of the type comprising a drive shaft, a forward clutch arranged essentially coaxially with respect to the drive shaft, a pinion of a first gearing stage or train which can be coupled by means of the forward clutch with the drive shaft, and two mutually parallel gears of the first gearing stage which are continuously in meshing engagement with the pinion of the first stage. Further, there is provided a power take-off shaft which is drivable by means of both gears of the first stage. Also there is provided a set of reversing gears composed of a number of reversing gears and at least one reverse clutch which likewise is coaxially arranged with respect to the drive shaft. With the forward clutch disengaged there is established a connection incorporating the set of reversing gears between the drive shaft and the gears of the first gearing stage.
Now with a state-of-the-art marine reversing gearing of this type, for instance as disclosed in U.S. Pat. No. 2,741,351, particularly FIGS. 3, 4 and 5, there is provided for the forward and rearward travel a respective first gearing stage each having its own pinion. Both of these pinions each independently mesh with two mutually parallelly mounted gears of the first stage which are rigidly connected with a respective pinion of the second gearing stage. Meshing with both pinions of the second stage is a common gear of the second stage which is rigidly connected by means of a power take-off shaft with a propeller of the ship. The pinion of the first stage provided for the forward or ahead travel is capable of being directly coupled or clutched by means of a forward clutch with a turbine driven-drive shaft. The pinion of the first stage provided for the rearward or astern travel is mounted parallel to the drive shaft and can be coupled by means of a first reverse clutch with a peripheral reversing gear and such meshes with a central reversing gear which is coaxially mounted with regard to the drive shaft. The central reversing gear, in turn, can be coupled by means of a second reverse clutch with the drive shaft. The mentioned clutches can be conjointly activated in such a manner that during disengagement of the forward clutch both of the reverse clutches are engaged, and conversely, during disengagement of both of the reverse clutches the forward clutch is engaged. There are used as the clutches simple dog or jaw clutches which are equipped with friction disks or self-synchronizing jaw clutches.
What has been found to be disadvantageous with such type arrangements is that in the case of dog or jaw clutches oftentimes the relative position of the teeth of the clutch which is to be engaged is such that the tooth gap and related tooth to be engaged do not coincide. Consequently, the clutch only then can be first engaged when the counter clutch--the forward or reverse clutch--has been completely disengaged.
However, this leads to the result that the drive turbine must be decoupled and therefore accelerated in rotational direction. In the case of rapidly accelerating gas turbines there therefore exists the danger that either the clutch which is to be engaged has too little time for engagement, or, however, the ends of the teeth which are to be engaged become damaged.
In FIG. 13 of the aforementioned U.S. Pat. No. 2,741,351 there is taught an arrangement employing self-synchronizing clutches which presupposes an absolute standstill of the shaft system, in order to avoid damage to the synchronization mechanism of the clutch which is to be engaged. This absolute standstill of the entire system only can be obtained with great difficulty and a reliable control of the operating state of the system requires the employment of considerable constructional means. Therefore, automation of the reversing operation is quite complicated and expensive.
A further drawback of a great many of the state-of-the-art reverse gearing or transmissions is the fact that such only can be coupled or clutched when the rotational moment of the turbine is greater than the negative propeller torque or rotational moment. This means that drive units must be available which can be rearwardly driven.